1. Field of Invention
The invention relates to a print head assembly capable of printing by scanning a print head in directions substantially orthogonal to the print medium conveyance direction.
2. Description of Related Art
Among well-known printer apparatuses for forming a predetermined print image on a print medium is an ink jet type printer apparatus having a print head that ejects ink to a recording sheet by driving piezoelectric elements through the application of a drive voltage thereto. In such an ink jet type printer apparatus, every time a recording sheet is conveyed, the print head is scanned in a direction substantially orthogonal to the conveying direction of the recording sheet and, at the same time, ink is ejected from nozzles at predetermined print times while the position of the print head being scanned is detected by an encoder device, or the like. Through this operation, the ink jet type printer apparatus is able to perform printing in a band unit.
For color printing, an ink jet type printer apparatus is equipped with print heads corresponding in number to different color inks, for example, black, cyan, magenta, yellow, and the like, that are arranged in the scanning direction. The nozzle intervals between the print heads (that is, intervals between nozzles of the print heads in the scanning direction) are set to a value obtained by multiplying the inverse number of the resolution by a natural number.
FIG. 9 shows an example wherein the resolution is 300 dpi and four print heads corresponding to black (K), cyan (C), magenta (M) and yellow (Y) are arranged so that the nozzle intervals between the print heads become a product of the inverse number (1/300 inch) of the resolution and a natural number (1 in the arrangement in FIG. 9). This arrangement makes it possible to position the nozzles of the print heads precisely at positions (print timing positions) at which dots are to be placed at that resolution (300 dpi) in the scanning direction of the print heads. Therefore, by outputting print timing signals from the encoder device to the print heads at, for example, every print timing position, a predetermined color print image can readily be formed.
However, when a plurality of colors need to be printed using the print head arrangement in which the nozzle intervals between the print heads are equal to a product of a natural number and the inverse number of the resolution, the print heads corresponding to the four colors, eject ink simultaneously at the same print time as indicated in FIG. 9. For example, if the four colors are required at a given print time, all the four print heads simultaneously eject ink. Simultaneous ink ejection from all the print heads at a print time requires a high level of drive voltage to the print heads at that print time. Such a peaky voltage requirement causes a significantly large load on the power source.